Series transformer.



G, A. BURNHAM. SERIES TRANSFORMER.

APPLICATION FILED 0CT.16. 1911.

1,1 38,625. 111101117011 Muy 11, 1915.

UNITED STATES OFFICE.

GEORGE A. BURNHAM, OF CLIFTONDALE, MASSACHUSETTS, ASSIGNOR TO SEARS B.

CONDIT, JR., 0F BROOKLINErMASSiCHUSETTS.

SERIES TRANSFORMER.

To all 11271 om it. m 11,1/ concern Be it known that I, Gi-:oncn A. BURNHAM, a citizen of the United States, residing at Cliftondale. in the county of Essex and State of Massachusetts, have invented certain new and useful Improvements in Series Transformers, of which the following is a full, clear, and exact specification.

This invention relates to series transformers, the object being to preserve a constant ratio of transformation and to prevent damage to the windings or to the instruments switch operating on excessive rise of voltage in the secondary circuit. The secondary is normally a. low tension circuit, but its potential is subject to wide changes under certain abnormal operating conditions, and especially on open circuit conditions or when the resistance is greatly increased. Under such circumstances the transformer becomes dangerouslyk hot and destroys the insulation producing a cross connection with the lowpotential apparatus, which leads to disastrous results. I provide means for cutting out the transformer .under dangerous conditions by opening the supplyy switch.

Thisapplication is a division of my parent application, No. 607,368, tiled Feb. u, 1911,` which fully sets forth the ai'lvantages of my improvements in maintaining the ratio of transformation.. The present application Vis restricted tothe control of the supply circuit fory the transformer, so that it may be cut out under dangerous conditions.

' In the accompanying drawings, Figure 1 shows diagrammatical y protective apparatus embodying my improvements. Fig. 2 shows another form ofthe same.

vr1 represents a series trans-former having primary coil 2 and a secondary coil 3. Such transformers commonly havel a high ratio of transformation and consist of an. iron core 4 Specification of Letters Patent.

Patented May 11, 1915.

Divided and this application filed October with a few turns of primary winding supplied by the high tension wires of the distribut-ion system. The secondary coil 3 has generally a greater' number of turns linking the same magnetic circuit and is carefully insulated from the primary winding. The ratio of transformation is governed by the relative number of turns of the two windings. In the primary winding there may be an extremely high voltage, but the voltage of the secondary winding is very low, being only sutlicient to force the proper amount of current through the indicating or recording instruments; therefore the high potential of the line which is dangerous to life is kept away from the switch-board.

The load carried by the secondary circuit is composed of electrical measuring instruments, one of which is indicated at 5, trip coils of circuit breakers, or other switchboard translating devices requiring a low potential current. In the case of a 20 to 1 ratio of transformation I make the primary of two layers of 15 turns each, which may be connected in series or parallel to supply diferent loads, and give the secondary 240 turns. A closed compensating circuit -6 maintains the ratio constant under wide load ranges so that the measuring instruments are free from error due to a falling otf of the current curve under such changes of load. This compensating coil is of low resistance and which may be adjustable; it may be used to supply the trip coil T of the automatic switch or thc latter may be operated by the secondary circuit as in Fig. 2. IV ith change of load in the secondary, such an auxiliary coil holds the ratio of transformation practically constant.

Itis exceedingly important that the transformers should be cut out of circuit when unusual conditions arise in the secondary, since the excessive heatot' the transformer will soon destroy it if the resistance of the secondary is greatly increased. In Fig. 1 I show means for opening the main circuit of the transformer through anv increased current flow in the compensating coil. Inv case the resistance of the secondary circuit increases unduly, which may follow froma loose connection of some ot' thev translating devices orother-cause, the entire load willi be In Fig. 2 the trip coil which operates the switch is 'supplied by the secondary of the transformer. In this arrangement, the switch is opened in case of overload in the primary circuit, and is also protected from excessive rise of voltage in the secondary circuit. The secondary supplies the trip coil, and a small relay 8 is placed in the compensating circuit. if the transformer is excessively loaded, the automatic switch having the trip coil 7 will be opened; or if there should be a break in -the external secondary circuit or any other trouble that would create an improper rise of secondary voltage the relay Willautomatically close the secondary circuit at a point near the transformer and hold the load constant thus preventing damage to the transformer.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. The combination of a' series transformer having a primary and a secondary normally deriving energy from the primary, a circuit connected to the primary, a switch in the primary circuit, a coil in inductive relation to the transformer rimary and secondary, 'and means contro led b said coil and'responsive to Wide changes o 'resistance and resultant excessive rise of voltage in the secondary for opening the switch.

2. The combination with a series transformer having a primary and a secondary normally, deriving energy :from the primary, of a circuit to which the primary is connected, an automatic switch in said-circuit, a trip coil) receiving its energy inductively from the transformer primary for opening the switch on overload, a coil in inductive vrelation to the transformer primary and secondary, and means controlled by the last mentioned coil for short-circuiting the secondary circuit upon excessive rise of resistance in the external secondary circuit.

3. The combination with a series trans former having a primary circuit and a secondary circuit normally fed therefrom, of a coil in inductive relation to the primary and secondary of the transformer and means controlled by said coil for preventing excessive rise of voltage in the secondary circuit.

4'. A series transformer having a primary winding, a secondary winding, and a closed coil on said transformer adapted to preserve its ratio of transformation under change of load, and means controlled by said coil for preventing excessive rise of voltage in the secondary circuit.

5. The combination with a series trans former having a primary winding, a secondary Winding, and a closed coil on said transformer adapted to preserve its ratio of transformation under change of load, of means controlled by said coil for preventing excessive rise of voltage in the secondary circuit, comprising an automatic switch in the primary circuit, and an overload trip coil for said switch receiving its energy inductively from the transformer primary.

In testimony whereof I aiiix my signature, in presence of two Witnesses.

GE'ORGE A.. BURNHAM.

Witnese s:

E. C. WATERHOUBE, CQC. Barnum.

Ai i) 

